Feds Find Big Flaws in Current Flood Maps

February 4, 2009

Flood maps for riparian areas and coastal zones are in need of significant improvement, according to a National Academies' National Research Council report released Jan. 23, 2009. The benefits of implementing the improvements would substantially outweigh the costs from deaths, property destruction, and repairs, the committee concluded.

The most urgently-needed upgrades for maps used by the Federal Emergency Management Agency (FEMA) involve obtaining and using high-accuracy and high-resolution land surface elevation data, and applying better terrain, wave, and surge data and models for coastal areas. Significant improvements in mapping and communications are also needed to accurately and effectively convey to the public the risks involved in living in or near a flood plain or coastal zone.

FEMA has been attempting to improve its flood maps. Despite expenditures of $1 billion, though, only about 1 of every 5 maps meets the agency's data quality standards. In order to improve its efforts, the agency asked the NRC to assess the situation, and make recommendations for improvements.

Based on detailed analysis of conditions in North Carolina and Florida, the NRC found that current data on topography can be off by at least 12 feet, and that resulting calculations of flood plains can be in error by 20% or more. The findings have direct implications throughout the country.

Fully implementing the report's findings will take many years. But the details in the report can provide useful hooks for investigating conditions in your community. Flooding has already occurred this year in portions of the country, such as the Pacific Northwest, and prime flooding season is just a few months away, giving you a small window of opportunity to do some pre-flood legwork.

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